lvmetad (cryptsetup?) problem after updating to 15.10

I just upgraded my laptop, with full disk encryption, to 15.10, and on rebooting it now hangs after the decryption passphrase is entered. It looks similar to Bug #148712, so might also involve cryptsetup, but it's not clear to me what the cause here is.

When hanging the screen reads:

/run/lvm/lvmetad.socket: connect failed: No such file or directory
WARNING: Failed to connect to lvmetad. Falling back to internal scanning.
Reading all physical volumes. This may take a while...
Found volume group "xubuntu-vg" using metadata type lvm2
/run/lvm/lvmetad.socket: connect failed: No such file or directory
WARNING: Failed to connect to lvmetad. Falling back to internal scanning.
2 logical volume(s) in volume group "xubuntu-vg" now active
fsck from util-linux 2.26.2
/dev/mapper/xubuntu--vg-root: clean, [etc...]

It then never gets to the login screen (waiting > 1 hour).

If I switch to the command line & login, I can see lvmetad.socket is there. So I don't know what to try - if the problem is the same asBug #148712 the fix is not clear to me either...